Numerous situations exist in which a body cavity needs to be catheterized to achieve a desired medical goal. One relatively common situation is to provide nutritional solutions or medicines directly into the stomach or intestines. A stoma is formed in the stomach or intestinal wall and a catheter is placed through the stoma. This surgical opening and/or the procedure to create the opening is common referred to as “gastrostomy”. Feeding solutions can be injected through the catheter to provide nutrients directly to the stomach or intestines (known as enteral feeding). A variety of different catheters intended for enteral feeding have been developed over the years, including some having a “low profile” relative to the portion of the catheter which sits on a patient's skin, as well as those having the more traditional or non-low profile configuration. These percutaneous transport catheters or tubes are frequently referred to as “gastrostomy tubes”, “percutaneous gastrostomy catheters”, “PEG tubes” or “enteral feeding catheters”.
To prevent the PEG tube from being pulled out of the stomach/intestinal wall, various types of retainers are used at a distal end of the catheter. Examples of conventional devices with Malecot tips or similar expanding tips are found at, for example, U.S. Pat. No. 3,915,171 for “Gastrostomy Tube” issued to Shermeta; U.S. Pat. No. 4,315,513 for “Gastrostomy and Other Percutaneous Transport Tubes” issued to Nawash et al.; U.S. Pat. No. 4,944,732 for “Gastrostomy Port” issued to Russo; and U.S. Pat. No. 5,484,420 for “Retention Bolsters for Percutaneous Catheters” issued to Russo. Exemplary commercial products include the Passport® Low Profile Gastrostomy Device available from Cook Medical, Inc. of Bloomington, Ind. and the Mini One™ Non-Balloon Button available from Applied Medical Technology, Inc. of Brecksville, Ohio. A shortcoming of these devices relates to the manner of insertion and withdrawal of a catheter or tube incorporating these retaining fixtures (e.g., a gastrostomy tube) into a body lumen such as into the stomach.
Balloons can be used in place of these conventional devices with Malecot tips or similar expanding tips. A balloon, typically made of a “soft” or elastomeric medical grade silicone, is attached to the end of the catheter and is deflated for insertion through the stoma and then inflated to hold the enteral feeding assembly in position. While these balloons have many advantages, balloons may eventually leak and deflate. In addition, “soft” or elastomeric medical grade silicone has a tendency to “creep” or stress relax over time which can change the dimensions of the balloon.
Various types of medical devices incorporating inflatable balloons devices are known and widely used in the medical field. For example, endotracheal tubes and tracheostomy tubes utilize inflatable balloons to create a seal that prevents the passage of mucus into the lungs. Pilot balloons, pressure gauges, and inflation indicators are used to provide a continuous reading of the pressure in the balloon in these devices. That is, these devices provide an output that conveys continuous or uninterrupted information showing pressure increases and decreases in the balloon. These devices are described at, for example, U.S. Pat. No. 3,642,005 for “Endotracheal Tube With Inflatable Cuff” issued to McGinnis.; U.S. Pat. No. 4,266,550 for “Pressure Indicators For Inflatable Cuff-Type Catheters” issued to Bruner.; U.S. Pat. No. 6,732,734 for “Pilot Balloon For Balloon Catheters” issued to Ogushi et al.; and U.S. Pat. No. 7,404,329 for “Pressure Gauge For Use With An Airway Lumen” issued to Quinn et al.
In addition to pilot balloons, pressure indicators incorporating bellows or diaphragms are known and electronic pressure indicators are known. For example, a simple bellows pressure indicator for showing continuous reading of fluid pressure is described in U.S. Pat. No. 3,780,693 for “Visible Fluid Pressure Indicator” to Parr. U.S. Pat. No. 7,383,736 “Device and Method for Pressure Indication” issued to Esnouf, describes a bellows device for use with a laryngeal mask balloon or other airway management equipment incorporating balloons. The device of Esnouf incorporates a bellows that is displaced by a differential pressure between the outside of the bellows and the inside of the bellows to provide a continuous reading of the increases and decreases in the pressure of fluid in the balloon. U.S. Pat. No. 7,018,359 for “Inner Pressure Indicator of Cuff” issued to Igarashi et al., describes a bellows or spring structure for use with a tracheostomy tube balloon or endotracheal tube. The device of Igarashi et al. is connected to the balloon through an inflation tube and has an inflation valve at the other end that is connected to a syringe. The device uses a bellows and/or spring indicator provide a continuous reading and display of the increase and decrease in the pressure of fluid in the balloon through movement of the bellows against a numerical scale printed on the housing. U.S. Pat. No. 5,218,970 for “Tracheal Tube Cuff Pressure Monitor” issued to Turnbull et al. describes a continuous pressure monitor for a tracheal tube incorporating an electronic pressure sensor such as a silicon strain gauge pressure sensor, a processor that performs various calibration, scaling and calculation operations on the signal from the sensor and provides an output to a numeric display conveying a continuous reading of the increases and decreases in the pressure of fluid in the balloon.
These indicators are adapted for airway devices where careful and constant monitoring of balloon pressure is important. In order to adequately seal the space between the lumen of the trachea and the balloon, there is a tendency to overinflate the balloon which may result in tissue damage. If the pressure is too low, the balloon does not adequately seal the space between the lumen of the trachea and the balloon thereby allowing secretions to enter the lungs causing pneumonia and other respiratory complications. In order to provide careful control of the balloon pressure, these pilot balloons, bellows and diaphragms indicators and electronic sensors are designed to convey a continuous reading of the increases and decreases in the pressure of fluid in the balloon.
While this level of sensitivity and continuous reading is desirable, pilot balloons and similar bellows or diaphragm indicators are relatively large and typically require skill and experience to accurately interpret the output of these conventional devices as they provide a continuous reading of pressure. While electronic pressure sensors are accurate and are generally easy to read, they are relatively large and expensive. Scaling these types of devices down to a sufficiently small size so they can be used with a low-profile PEG tube only highlights the problems associated with the size, calibration, accuracy, and reading or interpreting the output of these devices.
U.S. Pat. No. 6,878,130 for “External Inflation Indicator for a Low Profile Gastrostomy Tube” issued to Fournie et al. describes an external inflationary indicator similar to a pilot balloon integrated into the base of a gastrostomy device having a retainer balloon. The device of Fournie et al. provides a continuous tactile reading of the inflationary state of the retainer balloon. The Fournie et al. device utilizes two generally bubble-like portions that assume a generally convex shape when the retainer balloon is inflated and a generally concave shape when the balloon is deflated. The changing shape of these generally bubble-like portions provides a continuous tactile indication or reading of the inflationary state of the balloon. In addition, the external inflationary indicator provides continuous visual indication of the inflationary state of the retainer balloon through the use of a separating bar dividing these two generally bubble-like portions of the indicator. The separating bar visually separates as the balloon becomes fully inflated to indicate the inflationary state. Such continuous indication of the inflationary state is important for conventional PEG tube retainer balloons made of elastic materials such as “soft” or elastomeric medical grade silicone because these elastic materials must stretched to increase the balloon volume. Relatively large changes in pressure are needed to stretch such elastic materials from an un-stretched state to expand the balloon. Moreover, the relationship between the amount of pressure needed to stretch such elastic materials to expand the balloon and the volume of the balloon is nonlinear. That is, and the correlation between the pressure of the fluid inside the balloon and the volume of the balloon is not simple which leads to the use of continuous indicators designs such as those described by Fournie et al., if any indicator is used at all.
For example, FIG. 1A is an illustration of a conventional PEG tube device 10 having a base 12 and retainer balloon 13 made of conventional “soft” or elastomeric medical grade silicone in an un-stretched state (i.e., un-inflated condition). A pilot-balloon type indicator 15 as generally described by Fournie et al. is located in the base 12 of the conventional PEG tube device 10. FIG. 1B is an illustration of a conventional PEG tube device 10 having a base 12 and retainer balloon 13 made of conventional “soft” or elastomeric medical grade silicone which has been stretched by inflation to an inflated volume. A pilot-balloon type indicator 15 as generally described by Fournie et al. is located in the base 12 of the conventional PEG tube device 10. FIG. 1C is an illustration showing an exemplary relationship between the pressure of a fluid inside such an elastic retainer balloon and the balloon volume during the stretching the conventional “soft” or elastomeric medical grade silicone forming the balloon by increasing the pressure of a fluid inside the balloon. The illustration is a pressure versus volume plot for a Kimberly-Clark® Mic-Key® 12 french low profile gastrostomy feeding tube with a silicone balloon. As can be seen in FIG. 1C, stretching such elastic balloons from negligible volume (i.e., a deflated condition) at negligible pressure to a deployed volume between about 3 to about 5 milliliters requires an initially large and continuous change in pressure to overcome the resistance to stretching. In this example, an immediate pressure change from zero or negligible pressure to between about 4 to 7 pounds per square inch (28 to 48 kilopascals) is needed to overcome the resistance to stretching needed to inflate such exemplary conventional retainer balloons to a volume of even 1 cubic centimeter (approximately 1 milliliter) and a pressure between about 5 to 10 pounds per square inch (34 to 69 kilopascals) to inflate such conventional “soft” or elastomeric medical grade silicone balloons to a volume of about 3 cubic centimeters (˜3 milliliters) with sterile water—although saline solution or air can be used.
Integrating a pilot-balloon type indicator such as described by Fournie et al. or a bellows system or similar graduated indicator as previously described into the base of a low-profile PEG tube device which provides a continuous reading of the pressures encountered by such elastic balloons during stretching requires separating bars, indicator lines or similar components on the flexible membrane that provide information based on very small movements—typically less than one millimeter. Using such a small scale to provide a continuous reading of the inflationary state of the retainer balloon makes it difficult to read and view properly, especially at inflating pressure less than 4 pounds per square inch (less than 28 kilopascals). For example, the base of a typical low-profile PEG tube is approximately 1.625 inches (˜41 mm) in length, approximately 0.75 inches (˜19 mm) in width and approximately 0.5 inches (˜13 mm) in depth. Referring to FIG. 1D which corresponds to FIG. 3 of Fournie, et al., comparing the relative dimensions of the pilot-balloon type indicator 15 located in the base 12 of the conventional PEG tube device 10 with the base dimensions noted above provides a context in which to understand that the small size of the pilot-balloon type indicator 15 would be impractical. For example, the pilot-balloon type indicator would appear to have dimensions of approximately 6 mm in length, approximately 5 mm in width and the separating bar on the indicator would appear to have a width of approximately 0.8 mm (about the diameter of the medium size ball-tip from the tip of a ball point pen or the diameter of a pencil lead from a mechanical pencil).
Accordingly, there is a need for a pressure change indicator assembly that can be readily integrated into the head of a PEG tube and which is easy to view and read properly and function at pressures less than about 4 pounds per square inch (28 kilopascals). A need exists for a pressure change indicator assembly that be readily integrated into a PEG tube that is simple, reliable and accurate at indicating predetermined volumes as well as easy to understand. A need also exists for a pressure change indicator assembly that be readily integrated into a PEG tube that is simple, reliable and accurate at indicating predetermined pressures as well as easy to understand. There is also an unmet need for a pressure change indicator assembly that conveys a simple and easy to see and understand signal about a change in a deployed balloon, particularly in a balloon deployed at pressures less than about 4 pounds per square inch (28 kilopascals).